Research is proposed to increase our understanding of sperm capacitation and fertilization. Emphasis is to be placed on defining artificial and physiological requirements of rabbit sperm for the achievement of fertilizing ability, which will be assessed primarily in vitro. Morphological studies, including electron microscopy, will enable the assessment of experimental effects on the gametes and on the fertilization process. Biochemical and immunological studies of factors from the male and female reproductive tracts which affect capacitation negatively or positively will be identified and characterized. Biochemical mechanisms involved in sperm capacitation, including removal or alteration of surface components and metabolic changes, especially $ regarding cyclic AMP and adenyl cyclase, will be investigated. Efforts are proposed to improve conditions for fertilization in vitro and the potential for normal development after embryo transfer.